The role of beta Arg(-10) in the B800 bacteriochlorophyll and carotenoid pigment environment within the light-harvesting LH2 complex of Rhodobacter sphaeroides
The role of beta Arg(-10) in the B800 bacteriochlorophyll and carotenoid pigment environment within the light-harvesting LH2 complex of Rhodobacter sphaeroides
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DOI：
10.1021/bi9626315
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发表时间：
1997-09-16
期刊：
影响因子：
2.9
通讯作者：
Hunter, CN
中科院分区：
文献类型：
--
作者：
Fowler, GJS;Hess, S;Hunter, CN
先前的工作已经表明β Arg（-10）残基形成球形红细菌的LH 2复合物中B800细菌叶绿素的结合位点的一部分[Crielaard，W.，菲舍斯河W.，福勒湾，澳-地J. S.，货车Grondelle河，海灵沃夫湾J.，亨特角N.（1994）Biochim. Biophys. Acta 1183，473-482]，并且这与随后获得的来自嗜酸红球藻的相关LH 2复合物的X射线晶体学数据一致[McDermott，G.，Prince，S. M.，Freer，A.一、Hawthornthwaite-Lawless，A. M.，Papiz，M. Z.，科格德尔河J.，Isaacs，N. W.（1995）Nature 374，517-521]。因此，为了获得更多关于B800结合位点及其对B800吸收带的影响的信息，β Arg（-10）被替换为残基Met、His、Asn、Leu和Lys（除了我们先前工作中描述的Glu突变体）;这些残基被认为代表了适当范围的氨基酸形状、电荷和氢键能力。这种新的一系列β Arg（-10）突变体，在天然膜中以LH 2复合物的形式存在，已经使用各种生物化学和光谱技术进行了表征，以确定突变体与野生型（WT）LH 2不同的方式。例如，发现大多数突变体LH 2复合物在77 K下具有蓝移的B800吸收带，范围为794至783 nm;这种趋势的例外是β Arg（-10）至Met突变体，其在798 nm处吸收最大。这些蓝移减少了“B800”和B850色素之间的光谱重叠，这使我们能够通过进行一系列室温亚皮秒能量转移测量来检查β Arg（-10）突变体LH 2复合物的B800到B850转移步骤的性质。这些测量的结果表明，减少的重叠导致B800到B850的转移较慢，尽管发现β Arg（-10）的改变对LH 2内的内部能量转移效率几乎没有影响。类似地，类胡萝卜素到细菌叶绿素的能量转移在很大程度上不受影响，尽管注意到类胡萝卜素区域中激发光谱的偏移。这些β-精氨酸（-10）突变体复合物提供了一个机会，调查单体细菌叶绿素的结合的结构要求，并检查的基础上看到的细菌叶绿素在光合复合物的红移，除了提供新的信息环境的类胡萝卜素色素在这个复杂的。
Previous work has suggested that the beta Arg(-10) residue forms part of the binding site for the B800 bacteriochlorophyll in the LH2 complex of Rhodobacter sphaeroides [Crielaard, W., Visschers, R. W., Fowler, G. J. S., van Grondelle, R., Hellingwerf, K. J., Hunter, C. N. (1994) Biochim. Biophys. Acta 1183, 473-482], and this is consistent with the X-ray crystallographic data that have been subsequently obtained for the related LH2 complex from Rhodopseudomonas acidophila [McDermott, G., Prince, S. M., Freer, A. A., Hawthornthwaite-Lawless, A. M., Papiz, M. Z., Cogdell, R. J., Isaacs, N. W. (1995) Nature 374, 517-521]. Therefore, in order obtain more information about the B800 binding site and its effect on the B800 absorption band, beta Arg(-10) was replaced by residues Met, His, Asn, Leu, and Lys (in addition to the Glu mutant described in our previous work); these residues were thought to represent a suitable range of amino acid shape, charge, and hydrogen-bonding ability. This new series of beta Arg(-10) mutants, in the form of LH2 complexes in the native membrane, has been characterized using a variety of biochemical and spectroscopic techniques in order to determine the ways in which the mutants differ from wild-type (WT) LH2. For example, most of the mutant LH2 complexes were found to have blueshifted B800 absorption bands ranging from 794 to 783 nm at 77 K; the exception to this trend is the beta Arg(-10) to Met mutant, which absorbs maximally at 798 nm. These blue shifts decrease the spectral overlap between the ''B800'' and B850 pigments, which allowed us to examine the nature of the B800 to B850 transfer step for the beta Arg(-10) mutant LH2 complexes by carrying out a series of room temperature subpicosecond energy transfer measurements. The results of these measurements demonstrated that the reduced overlap leads to a slower B800 to B850 transfer, although the alterations at beta Arg(-10) were found to have little effect on the efficiency of internal energy transfer within LH2, Similarly, carotenoid to bacteriochlorophyll energy transfer was largely unaffected, although shifts in the excitation spectra in the carotenoid region were noted. These beta Arg(-10) mutant complexes provide an opportunity to investigate the structural requirements for the binding of monomeric bacteriochlorophyll and to examine the basis of the red shift seen for bacteriochlorophyll in photosynthetic complexes, in addition to providing new information about the environment of the carotenoid pigments in this complex.